Process for the preparation of high purity metallic titanium

ABSTRACT

HIGH PURITY METALLIC TITANIUM SPONGE WHICH HAS AN EXTREMELY LOW HYDROGEN GAS CONTENT PRODUCED BY REDUCING TITANIUM HALIDES WITH A METALLIC ALKALI METAL AT A TEMPERATURE OF BETWEEN 600* C. AND 800* C., DIGESTING AT OVER 900* C. FOR AT LEAST ONE HALF HOUR AND LEACHING WITH AN AQUEOUS SOLUTION.

3,669,648 Patented June 13, 1972 United States Patent 015cc US. Cl. 75-845 7 Claims ABSTRACT OF THE DISCLOSURE High purity metallic titanium sponge which has an extremely low hydrogen gas content produced by reducing titanium halides with a metallic alkali metal at a temperature of between 600 C. and 800 C., digesting at over 900 C. for at least one half hour and leaching with an aqueous solution.

EXPLANATION OF THE INVENTION The present invention relates to a process for the preparation of metallic titanium which comprises reducing tituanium tetrachloride with an alkali metal so as to provide metallic titanium which has a very minor hydrogen gas content and a low Brinell hardness.

Generally speaking, there are two processes for producing metallic titanium by reducing titanium tetrachloride with an alkali metal, i.e., a process by one reaction step which comprises causing titanium tetrachloride to react with an approximately stoichiometrical amount of an alkali metal and thereby reducing it to titanium metal by a one stage method, and another process by two reaction steps which comprises causing titanium tetrachloride to react with a stoichiometrically insuificient amount of an alkali metal and producing a lower valency titanium chloride as the first step and further, adding a deficient amount of alkali metal to the said chloride for reducing it.

As a process for separating titanium metal from a reaction mixture produced in the above mentioned processes, a leach treatment is usually carried out in such a manner that the said reaction mixture is rinsed with a DETAILED large amount of water and alkali chloride in the said reaction mixture is made to eluviate and removed therefrom. But, metallic titanium sponge obtained by the said leach treatment contains a substantial amount of hydrogen and in the case of using the sponge for arc-melting hydrogen is separated and the thereby, the arc can not be stabilized. Further, there is a danger of explosion and safety of the melting operation is impaired and furthermore, the finished product has drawbacks, e.g. undesirably high Brinell hardness.

In order to avoid this drawback, for example, Japanese patent publication No. 4304/1958 discloses using stoichiometrically, slightly insufiicient amounts of the alkali metal, to produce a metallic titanium sponge including a small quantity of low valency titanium chloride in the reaction compound and then, leaching the compound with an aqueous solution of mineral acid containing soluble phosphite. According to this process, phosphorous acid is employed as the auxiliary raw material, so that the cost becomes expensive, and additionally, phosphorous acid is present in the waste solution produced in the leaching process and contains a large amount of alkali chloride, so that it is very diflicult to recover the alkali chloride from it.

Further, another Japanese publication No. 9858/1958 proposed to heat the sponge at a temperature of 400 to 980 C. under vacuum conditions in order to remove the hydrogen gas therefrom after treating the metallic titanium sponge including the alkali metal chloride with an aqueous solution; but this process has drawbacks, such as intricacy of operation, high cost of equipment and expensive production cost. Further, although a low value of the hardness as well as a low content of hydrogen are required for titanium metal, those aforementioned processes of the prior art are not able to give satisfactory results.

We investigated these processes intensively in order to obtain metallic titanium having a low hydrogen content and a low Brinell hardness in a one stage process. As a result, we have discovered that when the reaction temperature is controlled within a certain optimum range, high purity metallic titanium sponge having low Brinell hardness is obtained.

In other words, although a reduction of titanium tetrachloride by an alkali metal can be performed at a wide range of temperature from the melting temperature of the alkali metal to l,000 C., according to the present ins. vention, the temperature should be particularly selected in the range of from 600 to 800 C. in a first reaction stage which comprises making an alkali metal react with titanium tetrachloride and said temperature so as to reduce major portions of titanium tetrachloride to metallic titanium. Then, the reaction compound is heated at a temperature of from 900 to 950 C., as the second reaction stage, for a period of from 1 to 10 hours during which the first stage reaction compound is digested and the reaction is completed.

The metallic titanium sponge so obtained can be very easily freed from alkali chloride and other impurities in a leaching process. The present invention has the advantage of curtailment of operting time, and savings of chemicals and industrial water. Also, a high purity titanium metal which has a low value of Brinell hardness is obtained. In carrying out the above reaction, the amount of titanium tetrachloride used is selected to be 0.5 percent or more of the stoichiometric amount, preferably, from 1.0 percent to 2.0 percent excess stoichiometric amount in proportion to the quality of alkali metal used.

A metal sponge of titanium, so obtained shows a beautiful metallic lustre and a lower Brinell hardness.

The reason for the metallurgical reaction herein described is not entirely clear, but it is believed that when the main reducing reaction (the first reaction step) is carried out at the defined temperature range of 600 to 800 C. crystalline growth of metallic titanium favorably takes place and large size crystals are produced, so that the rinse in a leaching process is easily performed and further, as those crystals have inactive surfaces, the surfaces do not adsorb impurities, hydrogen gas.

Furthermore it is surmised that a minor amount of easily polluted, pulverized metallic titanium produced in a reducing step is oxidized into a low valency titanium chloride by applying the excess amount of titanium tetrachloride and said low valency titanium chloride can be easily removed in the leach treatment step. From this above reason, any agitation of the reaction mixture during the reducing step should be avoided because the agitation gives pulversized metallic titanium which diminishes the efiect of the present invention.

Formation of large size crystalline metallic titanium in accordance with the present invention is achieved only by performing the first reaction step i.e., reduction at a temperature of '600 to 800 C. If a temperature of below 600 C. is used, blackish titanium metal powder is produced and it requires a long time leaching process, and also, it has an active surface, so that it is apt to adsorb impurities or gas. On the other hand, if a temperature of over 800 C. is used, part of the high temperature treatment causes a local reaction, and some alkali chloride penetrates into the inner part of the titanium metal and it becomes hard to remove. In both cases, high purity of titanium metal can not be obtained.

The reaction temperature in the present invention is measured at a midpoint between central part of the reactor and its peripheral part and a protective tube which is provided with thermocouple thermometer is located at a symmetrical position in contrast with the inlet for the raw material and cm. upward from the surface of a reaction mixture. If the protective tube of the thermocouple is directly immersed in the reaction mixture, metallic titanium and alkali chloride are deposited and solidify on an external wall of the protective tube and a thick layer which tends to impair the thermal conductively is formed thereon, so that, it is difficult to accurately measure the temperature of the reaction system. Additionally the position of the thermocouple must be kept at all times at 10 cm. or higher from the surface of the reaction mixture. Therefore, as the surface is raised by introducing raw material into the reactor, the position of the thermocouple must be drawn up gradually.

When a stoichiometrically excess amount of titanium tetrachloride is used in the present invention, the excess is selected from 0.5 percent or more of the stoichiometric amount. Preferably the selected amount is one percent or more of the stoichiometric amount, or two percent or less of said amount. If an excessive amount of titanium tetrachloride is employed, the excess titanium tetrachloride is not only consumed in vain but the reaction compound must also be treated with a high concentration of rnineralacid in order to inhibit the formation of titanium chloride hydroxide in the leach step.

The alkali metal in accordance with the present invention is selected from sodium metal or potassium metal, but sodium metal is most desirable from an industrial viewpoint.

In accordance with the process herein contemplated, conduits for inert gas are provided in a reactor for the alkali metal and titanium tetrachloride and a thermocouple thermometer is provided. The air in the reactor is substantially replaced with argon gas. Then, the alkali metal is introduced in the reactor and reactor is heated at a temperature of 600 to 800 0., preferably at a temperature of 600 to 700 C. and then, titanium tetrachloride is gradually introduced by regulating the flow rate, so that a reaction temperature may be maintained in the range of 600 to 800 C. In the feed cycle, the total amount of alkali metal may be previously introduced into the reactor or a portion of the total alkali metal may be introduced simultaneously or alternately in the course of introducing titanium tetrachloride. Otherwise, a certain amount of reaction compound is previously placed in the reactor and then, alkali metal and titanium tetrachloride may be continuously introduced from one side and the reaction compound may be continuously taken out from the other side.

When the reaction temperature exceeds the defined range, the reactor is cooled by blowing cool air on the external wall of the reactor, and when the temperature goes below the specified range, the reactor is heated in order to keep the temperature at the range of 600 to 800 C. until the raw material is completely introduced into the reactor.

After the introduction of the titanium chloride has finished, a reaction compound is obtained and this reaction compound is heated at a temperature of 900 to 950 C. for a period of at least one half hour, preferably between 1 to 10 hours. Thus, the reaction is completed, and the alkali chloride and metallic titanium are allowed to separate. Then, the product is cooled and rinsed with a large amount of water or aqueous solution of dilute mineral acid, particularly an aqueous solution of hydrochloric acid and metallic titanium sponge having a metallic lustre and of high purity is thereby obtained.

In accordance with the process of the present invention, not only a superior quality of metallic titanium sponge which contains a very small quantity of hydrogen gas is obtained, but intricate reaction equipment is unnecessary. Furthermore, the operation is simple, there is a savings of time and labor, and also a saving of industrial water in the leach treatment step.

For the purpose of giving those skilled in the art a better understanding of the invention, the following illustrative examples are given:

EXAMPLE I 100 kg. of filtered, purified metallic sodium was charged into an iron reduction vessel under an argon gas atmosphere and the vessel was heated at 600 C. by means of an electric furnace. Then, 206 kg. of purified titanium tetrachloride was fed into the vessel by regulating the flow rate so the reaction temperature was kept in the range of 620 to 690 C.

In the course of about 6 hours, the feed operation was finished and then, the reduction vessel was gradually heated and the temperature inside the vessel was raised to 930 C. and the temperature was maintained for 5 hours and then, the vessel was cooled.

The amount of titanium tetrachloride employed is the stoichiometric quantity in which all titanium chloride is reduced to metallic titanium by the alkali metal fed into the vessel.

A reaction compound in the said reduction vessel was crushed to a moderate particle size of about 2 mesh by means of a jaw crusher. Then the pulverized compound was leached with an aqueous solution of one percent hydrochloric acid for 2 hours after which it was rinsed with water for 2 hours. Then, the pulversized compound was dried at 60 C. under vacuum condition and thereby, metallic titanium sponge was obtained.

Yield rate 93 percent. The metallic titanium sponge showed a gas Brinell hardness of 88 analysis by vacuummelting showed 0.030 percent of hydrogen.

EXAMPLE II The same reduction vessel in Example I was employed and 100 kg. of purified sodium metal was charged into the vessel under an argon gas atmosphere. The vessel was heated at 600 C. by means of an electric furnace and then, 209 kg. of titanium tetrachloride was fed into the reduction vessel by regulating the flow rate so that the reaction temperature was kept in the range of 650 to 730 C. In the course of about 5.5 hours, the feed operation was finished and then, the vessel was heated so that the temperature inside was kept at 950 C. The temperature was maintained for about 5 hours and the vessel was cooled. The amount of titanium tetrachloride employed as against the sodium metal was 1.5 percent in excess of a stoichiometrical amount. The product, because of the presence of low valency titanium chloride, sodium chloride showed a greenish color. The reaction compound in the reduction vessel was similarly treated by the same procedure as described in Example I. Thus, metallic titanium sponge obtained here indicated a Brinell hardness of and 0.0017 percent of hydrogen content.

EXAMPLE III The atmosphere inside the reduction vessel in Example I was satisfactorily replaced by argon gas and 30 kg. of purified sodium metal was charged into the vessel. The vessel was heated at 600 C. and then, 61 kg. of purified titanium tetrachloride was dropped into the vessel while keeping the reaction temperature in the range of 600 to 720 C. Then, 65 kg. of sodium metal and 138 kg. of titanium tetrachloride were further dropped into the vessel while keeping the reaction temperature in the range of 600 to 720 C. The amount of titanium tetrachloride employed as against sodium metal exceeded 2 percent over a stoichiometrical amount. When the feeding of the reagent was completed, the reduction vessel was heated, that the temperature inside the vessel was raised to 930 C. and the same temperature was kept continuously for 3 hours, and then, it was cooled to a room temperature. The reaction compound was crushed and then, it was similarly treated by the same process as described in Example I and metallic titanium sponge was thereby obtained. The metallic titanium indicated a Brinell hardness of 83 and 0.0022 percent of hydrogen content.

EXAMPLE IV For the purpose of comparison, the reaction was carried out by the same procedure as described in Example II with with the only exception that the reaction temperature was maintained in the range of 400 to 500 C. Otherwise, the same procedure was used for leaching the reaction compound. The titanium metal obtained indicated a Brinel hardness of 145 and 0.0136 percent of hydrogen content.

EXAMPLE V For the purpose of comparison the reaction was carried out by the same procedure as described in Example I with the only exception that the reaction temperature was maintained in the range of 800 to 780 C. Otherwise, the same procedure was employed for leaching the reaction compound. The titanium metal obtained indicated a Brinell hardness of 117 and 0.0104 percent of hydrogen content.

We claim:

1. A process for the preparation of high purity, low hydrogen metallic titanium which comprises:

(1) introducing metallic sodium into a reaction vessel in which an inert atmosphere is maintained;

(2) heating said vessel and the sodium therein to a temperature of 600 C. to 800 C.;

(3) gradually introducing a titanium halide into the hot sodium in said vessel, the rate of flow of titanium halide into said sodium being regulated so that the halide and sodium are maintained at a temperature between 600 C. and 800 C. while said sodium and said halide react;

(4) continuing the addition of titanium halide until at least 0.5% of said halide, in excess of the stoichiometric amount has been added;

6 (5) then elevating the temperature of the contents of said vessel, including the reaction product therein to between 900 C. and 950 C. and maintaining said temperature for at least one-half hour, and then; (6) recovering high purity low-hydrogen titanium sponge from the resulting post-heated reaction product by leaching said product with an aqueous solution.

2. A process for the preparation of high purity metallic titanium according to claim 1 wherein said titanium halide is titanium tetrachloride.

3. A process for the production of high purity metallic titanium according to claim 1 wherein the titanium halide is a lower valency titanium chloride.

4. A process for the production of high purity metallic titanium according to claim 1 wherein the alkali metal is metallic sodium.

5. A process for the production of high purity metallic titanium according to claim 1 wherein the metallic alkali is metallic potassium.

6. A process for the production of high purity metallic titanium according to claim 1 wherein the aqueous solution used for leaching is diluted hydrochloric acid.

7. A process for the preparation of high purity metallic titanium according to claim 1 wherein the reactions are carried out in the absence of any substantial agitation,

References Cited UNITED STATES PATENTS 2,148,345 2/ 1939 Freudenberg -845 2,890,953 6/1959 Hill et al. 75-845 2,934,427 4/ 1960 Tao 75-845 2,997,385 8/ 1961 Winter 75-845 3,039,866 6/ 1962 Takeuchi 75-845 3,146,094 8/ 1964 Hannan et al. 75-845 FOREIGN PATENTS 717,930 11/1954 Great Britain a- 75-845 REUBEN EPSTEIN, Primary Examiner 

